1. Field of the Invention
The present invention relates to a thin micro reforming apparatus. More particularly, the invention relates to a thin micro reforming apparatus which has a fuel inlet portion in a central portion thereof to supply drops of liquid fuel into an evaporator thereof and allows the liquid fuel to expand in a large space in the evaporator, thereby suppressing the increase of back pressure occurring during the evaporation of the liquid fuel. This prevents backflow of the fuel due to the back pressure and thus there is no need to increase the injection pressure of the fuel and induces good gas flow through the flow paths of the reforming apparatus, ultimately enhancing the reforming capacity of the reforming apparatus.
2. Description of the Related Art
Recently, there have been increased uses of portable small-sized electronic devices including mobile phones, Personal Digital Assistants (PDAs), digital cameras, notebook computers and the like. In particular, since the launch of Digital Multimedia Broadcasting (DMB) through the mobile phones, the portable small-sized terminals are required to have increased power capacity. Lithium ion secondary batteries used in general to date, which have capacity for two-hour viewing of DMB, are undergoing efforts to improve their capacity, but there have been growing expectations on small-sized fuel cells for a more fundamental solution.
In order to realize such a small-sized fuel cell, either direct methanol type in which methanol is directly supplied to a fuel electrode or reformed hydrogen fuel cell (RHFC) type in which hydrogen is extracted from methanol and supplied to a fuel electrode can be adopted. The RHFC type uses hydrogen as fuel as in Polymer Electrode Membrane (PEM) type, thus having advantages in terms of output, power capacity per volume and in that it requires no reactants besides water. However, the method requires a reformer, thus having a disadvantage for miniaturization.
In order for the fuel cell system to obtain high power output density, a reformer is required to convert liquid fuel into gaseous fuel such as hydrogen gas. The reformer includes an evaporating part for gasifying methanol, a reforming part for converting methanol into hydrogen via catalytic reaction at a temperature from 250° C. to 290° C., and a CO removing part for removing CO, a byproduct. In the reforming part, heat absorption reaction takes place and the temperature should be maintained from 250° C. to 290° C. Also in the CO removing part, the temperature should be maintained at about 170° C. to 200° C. to allow effective reaction.
As a conventional example, Japanese Patent Application Publication No. 2003-048701 discloses a reforming apparatus 200 as shown in FIG. 1. As shown in FIG. 1, such a conventional micro reforming apparatus 200 has an inner cavity 204 in an evaporating chamber 202 and a heater 206 for evaporation disposed in the cavity 204. The cavity 204 has a fuel spray 208 therein, which sprays a mixed liquid 210 of the fuel, methyl alcohol and water inside the cavity 204. The sprayed mixed liquid fuel 210 is heated by the heater 206 and evaporated. The gas produced by gasifying the mixed liquid 210 flows through a micro channel 212 and is reformed into hydrogen and carbon dioxide by a reforming catalyst 214 formed in the micro channel 212.
The conventional method is advantageous in that the fuel spray 208 provided at a fuel inlet portion sprays the fuel to increase the surface area of the fuel being reformed, thereby expediting the evaporation. Also, the fuel spray 208 sprays the fuel in the form of droplets, thereby increasing the ratio of the surface area of the fuel to the volume of the fuel. This allows efficient evaporation of the fuel given the same amount of heat.
However, the conventional technology entails burden of separate installation of the fuel spray 208 and a separate controller for regulating the amount of the fuel sprayed by the fuel spray 208. Therefore, the conventional structure is complex and has difficulty in miniaturization.
FIG. 2 illustrates another conventional reforming apparatus 250 suggested in Japanese Patent Application Publication No. 2005-166453. In this conventional technology, a fuel cell is miniaturized to enable efficient reformation of a large amount of fuel with a micro reforming apparatus. Also, a silicon substrate 252 has micro channels 254 and a reforming space 256 formed therein. Catalysts are formed in the micro channels 254 and the reforming space 256 to reform hydrocarbon fuel and generate hydrogen. The micro channels 254 and the reforming space 256 are covered by a cover plate 260.
However, in such a conventional reforming apparatus 250, liquid fuel expands as it is gasified, and thus a large-capacity, high-pressure pump (not shown) is required to inject the fuel into the channels 254.
FIG. 3 illustrates further another conventional reforming apparatus 350 suggested in Japanese Patent Application Publication No. 2004-89748. In this conventional technology, a flow path is expanded at a side of a substrate 351 to provide a gassifier 353. A reformer 354 and a CO remover 355 are disposed successively downstream of the gassifier 353, and a hydrogen outlet 360 is formed downstream of the CO remover 355. Even though the flow path is expanded in the gassifier 353, the conventional technology does not adequately address the problem of back pressure occurring as the liquid fuel is gasified and expanded.
Therefore, the conventional reforming apparatuses have disadvantages in that as the fuel is converted to gas in the evaporator, the volume of the fuel expands instantaneously and the back pressure has an influence toward the fuel inlet portion to interfere with the inflow of the fuel. Therefore, there is a need in the art for a thin micro reformer having an improved structure of the evaporator to allow fuel inflow at low pressure, and miniaturized with excellent reforming capacity.